Thermoplastic Resin Composition Having Excellent Reflectivity

ABSTRACT

A thermoplastic resin composition includes: a polyester resin; a white pigment; a core-shell structured impact modifier; and a modified polyolefin resin. The thermoplastic resin composition and a molded article formed from the same can exhibit excellent properties in terms of reflectance, reflectance maintenance at high temperature, and/or flexural strength.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.14/748,879, filed on Jun. 24, 2015, pending, and claims priority under35 USC Section 119 to and the benefit of Korean Patent Application10-2014-0079516, filed on Jun. 27, 2014, and Korean Patent Application10-2015-0078825, filed on Jun. 3, 2015, the entire disclosure of each ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a thermoplastic resin composition.

BACKGROUND

Light emitting diodes (LEDs) and organic light emitting diodes (OLEDs)are rapidly replacing existing light sources and are a focus ofattention due to outstanding energy efficiency and long lifespanthereof. Generally, light emitting diodes form a light emitting diodepackage together with components such as a reflector, a reflector cup, ascrambler, and a housing so as to maximize optical efficiency throughhigh reflectance. Such components are required to withstand hightemperature while minimizing deterioration in reflectance and whitenessdue to yellowing.

As engineering plastics, polyester resins, copolymers thereof, andblends thereof exhibit useful properties and are thus used in variousfields including interior/exterior materials for products. Particularly,polyester resins are used as a material for such components. Examples ofpolyester resins mainly used as a material for the components includehighly heat-resistant polyester resins. However, highly heat-resistantpolyester resins have problems of low crystallization rate, lowmechanical strength, and poor impact resistance, although the highlyheat-resistant polyester resins do not suffer from deformation at hightemperature and exhibit good discoloration resistance.

To overcome these problems, typically, additives such as inorganicfillers have been added to the polyester resins to enhance mechanicalstrength and impact resistance. However, when an excess of additivessuch as inorganic fillers is used, there is a concern of deteriorationin moldability, such as bleed-out.

A polyester resin composition has been developed wherein a polyolefincopolymer is included in a polyester resin to enhance discolorationresistance and impact resistance. However, such a polyester resincomposition also has problems of low crystallization rate, poormoldability and molding stability, and insufficient mechanicalproperties.

Therefore, there is a need for a thermoplastic resin composition whichhas excellent mechanical properties in terms of reflectance, reflectancemaintenance at high temperature, and flexural strength without sufferingthe above problems, and can thus be used for components for lightemitting diodes.

SUMMARY

Exemplary embodiments provide a thermoplastic resin composition that canhave excellent properties in terms of reflectance, reflectancemaintenance at high temperature, and/or flexural strength, and a moldedarticle formed from the same.

In exemplary embodiments, the thermoplastic resin composition includes:a polyester resin; a white pigment; a core-shell structured impactmodifier; and a modified polyolefin resin.

In exemplary embodiments, the thermoplastic resin composition mayinclude about 0.01 parts by weight to about 15 parts by weight of thecore-shell structured impact modifier and about 0.01 parts by weight toabout 10 parts by weight of the modified polyolefin resin based on about100 parts by weight of a base resin including the polyester resin andthe white pigment, wherein the weight ratio of the polyester resin tothe white pigment may range from about 0.1:1 to about 10:1.

In exemplary embodiments, the polyester resin may include a repeat unitrepresented by Formula 1:

wherein Ar is a C₆ to C₁₈ arylene group, R₁ and R₃ are the same ordifferent and are each independently a C₁ to C₁₀ linear alkylene group,and R₂ is a C₃ to C₁₂ cyclic alkylene group.

In exemplary embodiments, the white pigment may include at least one oftitanium oxide, zinc oxide, zinc sulfide, white lead, zinc sulfate,barium sulfate, calcium carbonate, and/or alumina.

In exemplary embodiments, the core-shell structured impact modifier mayinclude at least one of an acrylic compound and/or a silicon compound asa core component.

In exemplary embodiments, the modified polyolefin resin may include acopolymer of a monomer mixture including an olefin and a comonomerincluding at least one oxygen atom capable of forming a copolymertogether with the olefin.

In exemplary embodiments, the comonomer may include at least one of(meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate, hexyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl(meth)acrylate, glycidyl (meth)acrylate, benzyl (meth)acrylate, vinylacetate, and/or vinyl alcohol.

In exemplary embodiments, the modified polyolefin resin may include theolefin in an amount of about 40 wt % to about 99 wt % based on the totalweight of the modified polyolefin resin.

In exemplary embodiments, the base resin may further include inorganicfillers.

In exemplary embodiments, the inorganic fillers may be present in anamount of about 1 wt % to about 40 wt % based on the total weight of thebase resin.

In exemplary embodiments, the inorganic fillers may include at least oneof glass fibers, carbon fibers, glass beads, glass flakes, carbon black,clay, kaolin, talc, mica, and/or wollastonite.

In exemplary embodiments, the weight ratio of the core-shell structuredimpact modifier to the modified polyolefin resin may range from about0.05:1 to about 20:1.

Other exemplary embodiments of the present invention relate to a moldedarticle. The molded article is formed from the thermoplastic resincomposition as set forth above.

In exemplary embodiments, the molded article may have a difference inreflectance of about less than 15, as measured before/after lightirradiation (LED light source, wavelength of about 450 nm) in a constanttemperature/humidity oven at about 170° C. and about 85% relativehumidity (RH) for about 1,000 hours, and a flexural strength at breakpoint of about 20 N to about 80 N, as measured by applying compressiveforce at a rate of about 1 mm/min using a universal testing machine(UTM).

In exemplary embodiments, the molded article may be a reflector and/orreflector cup for LEDs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a semiconductor device including areflector cup formed from a thermoplastic resin composition according toan exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail.

It should be understood that the following embodiments are provided forcomplete disclosure and thorough understanding of the invention by thoseskilled in the art. In addition, unless otherwise stated, technical andscientific terms as used herein have a meaning generally understood bythose skilled in the art. Descriptions of known functions andconstructions which may unnecessarily obscure the subject matter of thepresent invention will be omitted.

A thermoplastic resin composition according to the present inventionincludes: (A) a polyester resin; (B) a white pigment; (C) a core-shellstructured impact modifier; and (D) a modified polyolefin resin.

(A) Polyester Resin

According to exemplary embodiments of the present invention, thepolyester resin can enhance heat resistance, mechanical strength, and/orimpact resistance of the thermoplastic resin composition even at hightemperature.

In exemplary embodiments, the polyester resin may be an aromaticpolyester resin. The aromatic polyester resin is a polymer whichincludes a ring-shaped structure and thus has a high melting point. Thearomatic polyester resin may have a melting point of about 200° C. orhigher, for example, about 220° C. to about 380° C., and as anotherexample about 260° C. to about 320° C. In exemplary embodiments, thearomatic polyester resin may be a resin obtained by polycondensation ofa dicarboxylic acid component including an aromatic dicarboxylic acidand/or a derivative thereof with a C₂ to C₂₂ diol component.

In exemplary embodiments, the dicarboxylic acid component may includeterephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid, without being limited thereto. These may be usedalone or in combination thereof.

In exemplary embodiments, the diol component may include an alicyclicdiol to form a ring-shaped repeat unit. For example, the alicyclic diolmay include a C₅ to C₂₂ cycloaliphatic diol, such as but not limited to1,4-cyclohexanedimethanol (CHDM) and the like. The alicyclic diol mayhave trans/cis isomer ratio of about 2.3 to about 10, for example, about2.5 to about 5. Within this range, the polyester resin can haveexcellent heat resistance, and the thermoplastic resin composition canexhibit excellent moldability, mechanical properties, discolorationresistance, and/or photostability.

In addition to the alicyclic diol, the diol component may furtheroptionally include ethylene glycol (EG), which is an aliphatic diol.When the diol component includes ethylene glycol, the ethylene glycolmay be present in an amount of 85 wt % or less, for example, about 20 wt% to about 70 wt % based on the total weight (100 wt %) of the diolcomponent. In some embodiments, the diol component may include ethyleneglycol in an amount of 0 (ethylene glycol is not present), about 0(ethylene glycol is present), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, or85 wt %. Further, according to some embodiments of the presentinvention, the amount of ethylene glycol can be in a range from aboutany of the foregoing amounts to about any other of the foregoingamounts.

Within this range, the diol component can enhance impact resistance ofthe polyester resin with minimal or no deterioration in heat resistanceof the polyester resin.

In addition to the alicyclic diol, the diol component may furtheroptionally include a C₆ to C₂₁ aromatic diol, a C₃ to C₈ aliphatic diol,or a mixture thereof. Examples of the C₆ to C₂₁ aromatic diol mayinclude 2,2-bis-(3-hydroxyethoxyphenyl)-propane and2,2-bis-(4-hydroxypropoxyphenyl)-propane, and examples of the C₃ to C₈aliphatic diol may include propane-1,3-diol, butane-1,4-diol,pentane-1,5-diol, hexane-1,6-diol, 3-methylpentane-2,4-diol,2-methylpentane-1,4-diol, 2,2,4-trimethylpentane-1,3-diol,2-thylhexane-1,3-diol, and 2,2-diethylpropane-1,3-diol, without beinglimited thereto. These may be used alone or in combination thereof.

The C₆ to C₂₁ aromatic diol, the C₃ to C₈ aliphatic diol, or the mixturethereof may be present in an amount of about 3 wt % or less based on thetotal weight (100 wt %) of the diol component. In some embodiments, thediol component may include the C₆ to C₂₁ aromatic diol and/or C₃ to C₈aliphatic diol in an amount of 0 (the C₆ to C₂₁ aromatic diol and/or C₃to C₈ aliphatic diol is not present), about 0 (the C₆ to C₂₁ aromaticdiol and/or C₃ to C₈ aliphatic diol is present), 1, 2, or 3 wt %.Further, according to some embodiments of the present invention, theamount of the C₆ to C₂₁ aromatic diol and/or C₃ to C₈ aliphatic diol canbe in a range from about any of the foregoing amounts to about any otherof the foregoing amounts.

Examples of the polyester resin may include without limitation apolyethylene terephthalate resin, a polytrimethylene terephthalateresin, a polybutylene terephthalate resin, a polyhexamethyleneterephthalate resin, a polycyclohexane dimethylene terephthalate resin,and an amorphous modified polyester resin thereof. These may be usedalone or as a mixture thereof. One example of the mixture may include amixture of a polyethylene terephthalate resin and a polybutyleneterephthalate resin.

In some embodiments, the polyester resin may include a repeat unitrepresented by Formula 1.

In Formula 1, Ar is a C₆ to C18 arylene group, R₁ and R₃ are the same ordifferent and are each independently a C₁ to C₁₀ linear alkylene group,and R2 is a C₃ to C₁₂ cyclic alkylene group. Here, R₁, R₂, and R₃ arederived from an alicyclic diol and may have a total carbon number of 5to 22.

In exemplary embodiments, the polyester resin may include apolycyclohexylenedimethylene terephthalate (PCT) resin represented byFormula 2, without being limited thereto.

In Formula 2, m is an integer from 10 to 500.

In exemplary embodiments, the (A) polyester resin may have an intrinsicviscosity [η] of about 0.4 dl/g to about 1.5 dl/g, for example, about0.5 dl/g to about 1.2 dl/g, as measured at about 35° C. using ano-chlorophenol solution (concentration: about 0.5 g/dl). Within thisrange, the polyester resin composition can exhibit excellent mechanicalproperties and/or moldability.

In exemplary embodiments, the polyester resin may be prepared by apolycondensation method known in the art. For example, thepolycondensation method may include direct condensation of an acidthrough transesterification using a glycol or a low grade alkyl ester,without being limited thereto.

In exemplary embodiments, the polyester resin may have a weight averagemolecular weight of about 3,000 g/mol to about 30,000 g/mol, forexample, about 5,000 g/mol to about 20,000 g/mol, as measured by gelpermeation chromatography (GPC). Within this range, the composition canexhibit excellent moldability and mechanical properties.

(B) White Pigment

According to exemplary embodiments of the present invention, the whitepigment can enhance whiteness and/or reflectance of the polyester resincomposition, and/or can improve discoloration resistance and/orphotostability of the composition even under high temperature conditionsthrough combination with other components. The white pigment may includeany typical white pigments without limitation. Examples of the whitepigment may include without limitation titanium oxide, zinc oxide, zincsulfide, white lead (2PbCO₃.Pb(OH)₂), zinc sulfate, barium sulfate,calcium carbonate, alumina, and the like. These may be used alone or incombination thereof

In exemplary embodiments, the white pigment may include titanium oxide,which can exhibit high whiteness, high light reflectance, highdispersibility, excellent weather resistance, and/or chemical stabilitythrough combination with other components. Titanium oxide can have anycrystal structure without limitation. In exemplary embodiments, titaniumoxide can have a rutile and/or tetragonal crystal structure, which canbe stable upon exposure to high temperature for a long time and/or caneffectively prevent deterioration in reflectance of the polyester resincomposition.

In exemplary embodiments, the white pigment may have an average particlediameter about 0.01 μm to about 2.0 μm, for example, about 0.05 μm toabout 0.7 μm. Within this range, the resin composition can exhibitexcellent properties in terms of whiteness, reflectance, and the like.

In exemplary embodiments, the white pigment may be subjected to surfacetreatment with an organic surface treatment agent and/or an inorganicsurface treatment agent. Examples of the organic surface treatment agentmay include without limitation silane coupling agents,polydimethylsiloxane, trimethylolpropane (TMP), pentaerythritol, and thelike. These may be used alone or in combination thereof. Examples of thesilane coupling agents may include without limitationvinyltriethoxysilane, 2-aminopropyltriethoxysilane,2-glycidoxypropyltriethoxysilane, and the like. Examples of theinorganic surface treatment agents may include without limitationaluminum oxide (alumina, Al₂O₃), silicon dioxide (silica, SiO₂),zirconia (zirconium dioxide, ZrO₂), sodium silicate, sodium aluminate,sodium aluminum silicate, zinc oxide, mica, and the like. These may alsobe used alone or in combination thereof. Upon surface treatment, theorganic and/or inorganic surface treatment agent may be present in anamount of less than 5 parts by weight based on about 100 parts by weightof the white pigment. Within this range, the resin composition canexhibit further enhanced whiteness and/or reflectance.

A base resin according to the present invention includes the polyesterresin and the white pigment, wherein a weight ratio of the polyesterresin to the white pigment may range from about 0.1:1 to about 10:1, forexample, about 2:1 to about 10:1. Within this range, the base resin canexhibit excellent heat resistance, moldability, mechanical properties,discoloration resistance, and/or photostability.

(C) Core-Shell Structured Impact Modifier

According to exemplary embodiments of the present invention, thecore-shell structured impact modifier can improve interface propertiesof the base resin, together with the modified polyolefin resin, therebyenhancing reflectance, reflectance maintenance at high temperature,and/or flexural strength of the thermoplastic resin composition. Thecore-shell structured impact modifier may be obtained by grafting ashell component to a core (rubber core) to form a shell.

In exemplary embodiments, the core component may include a siliconcompound, an acrylic compound, or a mixture thereof

In exemplary embodiments, the silicon compound may include acyclosiloxane compound, for example, hexamethylcyclotrisiloxane,octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,dodecamethylcyclohexasiloxane, trimethyltriphenylcyclotrisiloxane,tetramethyltetraphenylcyclotetrasiloxane, octaphenylcyclotetrasiloxane,and the like, and combinations thereof, without being limited thereto.Further, the silicon compound may also be used together with a curingagent such as trimethoxymethylsilane, triethoxyphenylsilane,tetramethoxysilane, and/or tetraethoxysilane.

Examples of the acrylic compound may include without limitation(meth)acrylic acid, esters thereof, alkyl ethacrylates, and the like,and combinations thereof. Examples of the acrylic compound may includewithout limitation methyl(meth)acrylate, ethyl (meth)acrylate,butyl(meth)acrylate, 2-ethylbutyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate,octyl(meth)acrylate, n-pentyl (meth)acrylate, vinyl(meth)acrylate,lauryl(meth)acrylate, methyl ethacrylate, ethyl ethacrylate, and thelike, and combinations thereof.

As used herein, unless otherwise stated, the term “(meth)acrylic acid”includes “acrylic acid” and “methacrylic acid”, and the term“(meth)acrylate” includes “acrylate” and “methacrylate”.

In exemplary embodiments, the core may be a polymer (rubbery polymer) ofthe silicon compound, a polymer (rubbery polymer) of the acryliccompound, or a copolymer (rubbery polymer) of the silicon compound andthe acrylic compound. The rubbery polymer (rubber) may have an averageparticle diameter about 0.1 μm to about 1 μm. Within this range, thethermoplastic resin composition can exhibit excellent impact resistanceand/or gloss.

In exemplary embodiments, the shell component grafted to the core mayinclude an unsaturated compound. Examples of the unsaturated compoundmay include without limitation an acrylic compound, an aromatic vinylcompound, a vinyl cyanide compound, a heterocyclic compound, and thelike, and combinations thereof.

In exemplary embodiments, the acrylic compound may be the same as theacrylic compound included in the core component, and examples thereofmay include without limitation (meth)acrylic acid, esters thereof, alkylethacrylates, and the like, and combinations thereof. Examples of theacrylic compound may include without limitation methyl (meth)acrylate,ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylbutyl (meth)acrylate,2-ethylhexyl (meth)acrylate, hexyl (meth)acrylate, heptyl(meth)acrylate, octyl (meth)acrylate, n-pentyl (meth)acrylate, vinyl(meth)acrylate, lauryl (meth)acrylate, methyl ethacrylate, ethylethacrylate, and the like, and combinations thereof.

In exemplary embodiments, the aromatic vinyl compound may includestyrene, C₁ to C₁₀ alkyl substituted styrene, halogen substitutedstyrene, and the like, and combinations thereof, without being limitedthereto. Examples of the alkyl substituted styrene may include withoutlimitation o-ethyl styrene, m-ethyl styrene, p-ethyl styrene, α-methylstyrene, and the like, and combinations thereof.

In exemplary embodiments, the vinyl cyanide compound may includeacrylonitrile, methacrylonitrile, ethacrylonitrile, and the like, andcombinations thereof, without being limited thereto.

In exemplary embodiments, the heterocyclic compound may include maleicanhydride, C1-C10 alkyl and/or phenyl N-substituted maleimide, and thelike, and combinations thereof, without being limited thereto.

In exemplary embodiments, in the core-shell structured impact modifier,the core may be present in an amount of about 20 wt % to about 99 wt %,for example, about 50 wt % to about 95 wt %, and the shell may bepresent in an amount of about 1 wt % to about 80 wt %, for example,about 5 wt % to about 50 wt %. Within this range, the thermoplasticresin composition may exhibit excellent properties in terms of impactresistance and the like.

In exemplary embodiments, the thermoplastic resin composition mayinclude the core-shell structured impact modifier in an amount of about0.01 parts by weight to about 15 parts by weight, for example, about 1part by weight to about 10 parts by weight, based on about 100 parts byweight of the base resin. In some embodiments, the thermoplastic resincomposition may include the core-shell structured impact modifier in anamount of about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09,0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12, 13, 14, or 15 parts by weight. Further, according to someembodiments of the present invention, the amount of the core-shellstructured impact modifier can be in a range from about any of theforegoing amounts to about any other of the foregoing amounts.

Within this range, the core-shell structured impact modifier can improveimpact resistance, weather resistance, and/or package flexural strengthof the thermoplastic resin composition.

(D) Modified Polyolefin Resin

The modified polyolefin resin is obtained by imparting a polar group tonon-polar polyolefin, and can enhance, together with the core-shellstructured impact modifier and the like, reflectance, reflectancemaintenance at high temperature, and/or flexural strength of thethermoplastic resin composition.

In exemplary embodiments, the modified polyolefin resin may be acopolymer of a monomer mixture including an olefin such as ethylene,α-olefin, and the like, and a comonomer including at least one oxygenatom capable of forming a copolymer together with the olefin. Examplesof the comonomer may include without limitation (meth)acrylic acid;alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl(meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate, andthe like; ethylenically unsaturated group-containing modified esterssuch as glycidyl (meth)acrylate; aryl (meth)acrylates such as benzyl(meth)acrylate; vinyl acetate; vinyl alcohol; maleic anhydride, and thelike, and combinations thereof. The modified polyolefin resin may be acopolymer of a monomer mixture further including an aromatic vinylmonomer such as styrene and/or a diene monomer, in addition to theolefin and the comonomer including at least one oxygen atom.

Examples of the modified polyolefin resin may include without limitationethylene-vinyl acetate (EVA) copolymers; acid and/or anhydride modifiedethylene-vinyl acetate copolymers; ethylene-alkyl (meth)acrylatecopolymers such as ethylene-methyl acrylate (EMA) copolymer,ethylene-ethyl acrylate (EEA), ethylene-butyl acrylate (EBA) copolymer,and the like; ethylene-glycidyl (meth)acrylate copolymers;ethylene-glycidyl (meth)acrylate-alkyl acrylate terpolymers;ethylene-vinyl alcohol copolymers; ethylene-hydroxyalkyl (meth)acrylatecopolymers; ethylene-acrylic acid copolymers; acid and/or anhydridemodified polyethylene; styrene-ethylene-butadiene-styrene (SEBS)copolymers; ethylene-propylene-diene monomer (EPDM) rubber; and thelike, and combinations thereof.

In exemplary embodiments, the modified polyolefin resin may be a maleicacid modified polyolefin resin obtained by grafting maleic anhydride toa polyolefin resin to impart a polar group thereto. The maleic acidmodified polyolefin resin may be prepared by a reactive extrusionprocess in which, using a twin screw extruder, peroxide is added to highdensity polyethylene (HDPE) having a melt-flow index (MI) of about 10g/10 min to about 50 g/10 min to break ethylene bonds and generate freeradicals, thereby introducing maleic anhydride (MAH) into the ethylenebonds.

In exemplary embodiments, the modified polyolefin resin may include theolefin in an amount of about 40 wt % to about 99 wt %, for example,about 50 wt % to about 98 wt %, and as another example about 60 wt % toabout 95 wt %, based on the total weight (100 wt %) of the modifiedolefin resin. Within this range, the thermoplastic resin composition canexhibit enhanced properties in terms of reflectance, mechanicalstrength, and the like.

In exemplary embodiments, the thermoplastic resin composition caninclude the modified polyolefin resin in an amount of about 0.01 partsby weight to about 10 parts by weight, for example about 0.1 parts byweight to about 5 parts by weight, based on about 100 parts by weight ofthe base resin. In some embodiments, the thermoplastic resin compositionmay include the modified polyolefin resin in an amount of about 0.01,0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 parts by weight.Further, according to some embodiments of the present invention, theamount of the modified polyolefin resin can be in a range from about anyof the foregoing amounts to about any other of the foregoing amounts.

Within this range, the modified polyolefin resin can enhance reflectancemaintenance at high temperature and/or package flexural strength of thethermoplastic resin composition.

In exemplary embodiments, the weight ratio of the core-shell structuredimpact modifier to the modified polyethylene may range from about 0.05:1to about 20:1, for example, about 1:1 to about 20:1. Within this range,the thermoplastic resin composition can exhibit further enhancedreflectance, reflectance maintenance at high temperature, and/orflexural strength.

The thermoplastic resin composition according to one embodiment of theinvention may further include inorganic filler in the base resin.

According to the present invention, the inorganic filler can improvemechanical strength of the thermoplastic resin composition, and mayinclude any inorganic filler known in the art. For example, theinorganic fillers may have a cross-section of various shapes, such as acircular shape, elliptical shape, and/or rectangular shape, and thelike.

Examples of the inorganic fillers may include without limitation glassfibers, carbon fibers, glass beads, glass flakes, carbon black, clay,kaolin, talc, mica, wollastonite, and the like, and combinations thereofIn view of mechanical properties, in exemplary embodiments, theinorganic fillers can include glass fibers.

In exemplary embodiments, the glass fibers may include circular glassfibers and/or glass fibers having a flake shape in cross-section. Thecircular glass fibers may have a cross-sectional diameter of about 5 μmto about 20 μm and a pre-processing length of about 2 mm to about 5 mm.The flake glass fibers may have a cross-sectional aspect ratio of about1.5 to about 10 and a pre-processing length of about 2 μm to about 5 μm.When such inorganic fillers are used, the resin composition can exhibitimproved processability and a molded article can exhibit significantlyimproved mechanical properties such as flexural strength, impactstrength, and the like.

In exemplary embodiments, the inorganic fillers may be subjected tosurface coating with a surface treatment agent to increase couplingforce to the polyester resin. Examples of the surface treatment agentmay include silane compounds, urethane compounds, and/or epoxycompounds, without being limited thereto.

In addition, the inorganic fillers may be used as a nucleating agent.For example, when the polyester resin composition further includes talcas the nucleating agent, the polyester resin composition has fastersolidification time upon injection molding due to faster crystallizationrate thereof, and can exhibit improved mechanical properties in terms offlexural strength.

In exemplary embodiments, the thermoplastic resin composition caninclude inorganic filler may be present in an amount of about 1 wt % toabout 40 wt %, for example, about 10 wt % to about 20 wt %, based on thetotal weight of the base resin. In some embodiments, the thermoplasticresin composition may include the inorganic filler in an amount of about1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38,39, or 40 wt %. Further, according to some embodiments of the presentinvention, the amount of the inorganic filler can be in a range fromabout any of the foregoing amounts to about any other of the foregoingamounts.

Within this range, the inorganic fillers can enhance mechanicalproperties, heat resistance, and/or moldability of the resin compositionwith minimum or no deterioration of other properties thereof.

According to exemplary embodiments of the present invention, the resincomposition may further include one or more typical additives withoutaffecting intended effects of the invention, as needed. Examples of theadditives may include antibacterial agents, heat stabilizers,antioxidants, releasing agents, photostabilizers, inorganic additives,surfactants, coupling agents, plasticizers, compatibilizers, lubricants,antistatic agents, colorants, pigments, dyes, flame retardants, flameretardant aids, anti-dripping agents, weather resistance stabilizers, UVabsorbers, UV blocking agents, and the like, and mixtures thereof,without being limited thereto.

In exemplary embodiments, examples of the antioxidants may includephenol, amine, sulfur, and/or phosphorus antioxidants; examples of theheat stabilizers may include lactone, hydroquinone, halogenated copper,and/or iodine compounds; and examples of the flame retardants mayinclude bromine, chlorine, phosphorus, antimony, and/or inorganiccompounds, without limitation.

The additives may be present in a proper amount with minimal or noeffect on properties of the polyester resin composition. In exemplaryembodiments, the additives may be present in an amount of about 20 partsby weight or less, for example, about 0.1 parts by weight to about 15parts by weight, based on about 100 parts by weight of the base resin.

The thermoplastic resin composition according to the present inventionmay be prepared by a method known in the art. For example, the abovecomponents and, optionally, other additives can be mixed using aHenschel mixer, a V blender, a tumbler blender, or a ribbon blender,followed by melt extrusion at about 150° C. to about 350° C. in a singlescrew extruder or a twin screw extruder, thereby preparing a resincomposition in pellet form. For example, the mixture of the componentsand the additive(s) can be subjected to extrusion under conditions of atemperature of about 250° C. to about 310° C., a screw rotating speed ofabout 300 rpm to about 600 rpm, and a self-feeding rate of about 60kg/hr to about 600 kg/hr using a twin screw extruder with L/D of about29 and φ of about 36 mm, thereby preparing a polyester resin compositionin pellet form.

A molded article according to the present invention is formed of thethermoplastic resin composition according to the present invention. Forexample, the molded article may be manufactured using the thermoplasticresin composition by a molding method known in the art, such asinjection molding, dual injection molding, blow molding, extrusion,thermoforming, and the like. The molded article formed of thethermoplastic resin composition can exhibit high reflectance and,particularly, excellent reflectance maintenance at high temperaturewhile exhibiting excellent flexural strength.

In exemplary embodiments, the molded article may have a difference inreflectance of about less than about 15, for example, about 1 to about10, as measured before/after light irradiation (LED light source,wavelength of about 450 nm) in a constant temperature/humidity oven atabout 170° C. and about 85% RH for about 1,000 hours, and a flexuralstrength at break point of about 20 N to about 80 N, for example, about25 N to about 60 N, as measured by applying compressive force at a rateof about 1 mm/min using a universal testing machine (UTM).

The molded article formed of the thermoplastic resin compositionaccording to the present invention can exhibit considerably enhancedmechanical strength including flexural strength and realize excellentreflectance through combination of the base resin, the core-shellstructured impact modifier, and the modified polyolefin resin. Thus, themolded article can be used for light reflection without limitation. Forexample, the molded article is useful as a reflector for a lightemitting device of electrical/electronic components, indoor/outdoorillumination devices, automotive lighting devices, displays, and thelike, particularly, a reflector or reflector cup for LEDs.

FIG. 1 is a sectional view of a semiconductor device (package) includinga reflector cup formed from a thermoplastic resin composition accordingto one embodiment of the invention. As shown in FIG. 1, thethermoplastic resin composition according to the invention may be formedinto a reflector or reflector cup 1 of various shapes, and the preparedreflector cup 1 may be assembled with various known electrodes 2,substrates 3, sealing resins 4, wires 5, and light emitting diodes(LEDs) 6 to form products including light emitting diodes (LEDs) ororganic light emitting diodes (OLEDs), such as semiconductor devices,illumination devices, and the like. In addition, the constitution as setforth above can be modified and changed in various ways by those skilledin the art.

Hereinafter, the present invention will be described in more detail withreference to the following examples. It should be understood that theseexamples are provided for illustration only and are not to be construedin any way as limiting the present invention.

EXAMPLES

Details of components used in the following Examples and ComparativeExamples are as follows:

(A) Polyester resin

Polycyclohexylenedimethylene terephthalate (PCT) resin (PCT0302, SKChemical) is used.

(B) White pigment

Titanium oxide (SAOMAI SM 2S15, Wooshin Pigment Co., Ltd.) is used.

(C) Core-shell structured impact modifier

(C1) A core-shell structured impact modifier obtained by grafting methyl(meth)acrylate to a butylacrylate rubber core available from MRC Co.,Ltd. (average particle diameter: 150 μm to 250 μm) to form a shell isused.

(C2) A core-shell structured impact modifier obtained by grafting methyl(meth)acrylate to a polydimethylsiloxane rubber core available from MRCCo., Ltd. (average particle diameter: 150 μm to 250 μm) to form a shellis used.

(D) Modified polyolefin resin

An ethylene-methylacrylate (EMA) copolymer having an ethylene content of70 wt % is used.

(E) Glass fiber

A glass fiber having a circular section, a sectional diameter of 10 μm,and an average length of 3 mm (910, Owens Corning Co., Ltd.) is used.

Example 1

As listed in Table 1, 100 parts by weight of a base resin including 75wt % of the (A) polyester resin and 25 wt % of the (B) white pigment, 3parts by weight of the (C1) core-shell structured impact modifier, and0.2 parts by weight of the (D) modified polyolefin resin are subjectedto dry blending to prepare a thermoplastic resin composition. Then, thethermoplastic resin composition is subjected to extrusion at a nozzletemperature of 250° C. to 350° C. using a twin screw extruder (φ=45 mm),thereby preparing pellets. The prepared pellets are dried at 100° C. for4 hours or more, followed by injection molding, thereby preparing aspecimen. The prepared specimen is evaluated as to reflectance,difference in reflectance, and flexural strength by the followingmethods. Results are shown in Table 2.

Example 2

As listed in Table 1, 100 parts by weight of a base resin including 60wt % of the (A) polyester resin, 20 wt % of the (B) white pigment, and20 wt % of the (E) glass fiber, 3 parts by weight of the (C1) core-shellstructured impact modifier, and 0.2 parts by weight of the (D) modifiedpolyolefin resin are subjected to dry blending to prepare athermoplastic resin composition. Then, the thermoplastic resincomposition is subjected to extrusion at a nozzle temperature of 250° C.to 350° C. using a twin screw extruder (φ=45 mm), thereby preparingpellets. The prepared pellets are dried at 100° C. for 4 hours or more,followed by injection molding, thereby preparing a specimen. Theprepared specimen is evaluated as to reflectance, difference inreflectance, and flexural strength by the following methods. Results areshown in Table 2.

Example 3

As listed in Table 1, 100 parts by weight of a base resin including 60wt % of the (A) polyester resin, 20 wt % of the (B) white pigment, and20 wt % of the (E) glass fiber, 3 parts by weight of the (C1) core-shellstructured impact modifier, and 0.5 parts by weight of the (D) modifiedpolyolefin resin are subjected to dry blending to prepare athermoplastic resin composition. Then, the thermoplastic resincomposition is subjected to extrusion at a nozzle temperature of 250° C.to 350° C. using a twin screw extruder (φ=45 mm), thereby preparingpellets. The prepared pellets are dried at 100° C. for 4 hours or more,followed by injection molding, thereby preparing a specimen. Theprepared specimen is evaluated as to reflectance, difference inreflectance, and flexural strength in by the following methods. Resultsare shown in Table 2.

Example 4

As listed in Table 1, 100 parts by weight of a base resin including 60wt % of the (A) polyester resin, 20 wt % of the (B) white pigment, and20 wt % of the (E) glass fiber, 3 parts by weight of the (C2) core-shellstructured impact modifier, and 0.5 parts by weight of the (D) modifiedpolyolefin resin are subjected to dry blending to prepare athermoplastic resin composition. Then, the thermoplastic resincomposition is subjected to extrusion at a nozzle temperature of 250° C.to 350° C. using a twin screw extruder (φ=45 mm), thereby preparingpellets. The prepared pellets are dried at 100° C. for 4 hours or more,followed by injection molding, thereby preparing a specimen. Theprepared specimen is evaluated as to reflectance, difference inreflectance, and flexural strength in by the following methods. Resultsare shown in Table 2.

Example 5

Preparation of a specimen and testing are performed in the same manneras in Example 2 except that the (C1) core-shell structured impactmodifier is used in an amount of 18 parts by weight based on 100 partsby weight of the base resin.

Example 6

Preparation of a specimen and testing are performed in the same manneras in Example 2 except that the (D) modified polyolefin resin is used inan amount of 12 parts by weight based on 100 parts by weight of the baseresin.

Comparative Example 1

Preparation of a specimen and testing are performed in the same manneras in Example 3 except that the (D) modified polyolefin resin is notincluded.

Comparative Example 2

Preparation of a specimen and testing are performed in the same manneras in Example 3 except that the (Cl) core-shell structured impactmodifier is not included.

Property Evaluation

1) Measurement of reflectance (unit: %) and difference in reflectance:Reflectance (specular component included (SCI) mode) upon lightirradiation at a wavelength of 450 nm (LED light source) is measured ona plate type specimen. As a reflectometer, 3600 CIE Lab available fromKonica Minolta Holdings, Inc. is used. In addition, after measuringreflectance of the specimen, the specimen is placed in a constanttemperature/humidity oven at 170° C. and 85% RH, followed by lightirradiation (LED light source, wavelength of 450 nm) for 1,000 hours andthen measuring reflectance after light irradiation under constanttemperature/humidity conditions, thereby calculating decrement(difference) in reflectance.

2) Measurement of package flexural strength (unit: N): With a 7032 (16cavity) mold mounted on an injection molding machine, a metal LED leadframe is insert molded to prepare a molded article. The prepared moldedarticle is cut into a single piece (specimen) using a hand cutter,followed by measuring compressive strength at a rate of about 1 mm/minusing a universal testing machine (UTM), thereby finding a flexuralstrength at break point.

TABLE 1 Comparative Comparative Example Example Example Example ExampleExample Example Example Item 1 2 3 4 5 6 1 2 (A) Polyester resin 75 6060 60 60 60 60 60 (wt %) (B) White pigment 25 20 20 20 20 20 20 20 (wt%) (E) Glass fiber (wt %) 0 20 20 20 20 20 20 20 (C1) Core-shell 3 3 3 —18 3 3 — structured impact modifier (parts by weight) (C2) Core-shell —— — 3 — — — — structured impact modifier (parts by weight) (D) Modifiedpolyolefin 0.2 0.2 0.5 0.5 0.2 12 — 0.5 resin (parts by weight) Parts byweight: Based on 100 parts by weight of base resin (A + B + E)

TABLE 2 Comparative Comparative Example Example Example Example ExampleExample Example Example Item 1 2 3 4 5 6 1 2 Reflectance Before constant94.9 94.0 94.4 94.2 94.7 94.4 93.1 93.2 (%) temperature/humidity testingAfter constant 87.1 85.8 86.5 86.4 86.9 85.4 74.8 75.7temperature/humidity testing Difference in 7.8 8.2 7.9 7.8 7.8 9.0 18.317.5 reflectance Package flexural strength (N) 29 49 53 52 34 38 35 32

From the results of Example 1 in Table 2, it can be seen that thethermoplastic resin composition according to the present inventionexhibits similar flexural strength to Comparative Examples 1 to 2despite not including glass fibers, has relatively high reflectance ascompared with Comparative Examples 1 to 2, and exhibits a relativelysmall difference in reflectance before/after constanttemperature/humidity testing and thus excellent reflectance maintenanceproperties at high temperature, as compared with those of ComparativeExamples 1 to 2. In addition, from the results of Examples 2 to 4 inTable 2, it can be seen that the thermoplastic resin compositionaccording to the present invention exhibits excellent properties interms of reflectance, reflectance maintenance at high temperature, andpackage flexural strength, when further including inorganic fillers suchas glass fibers.

Although some embodiments have been described herein, it should beunderstood that these embodiments are provided for illustration only andare not to be construed in any way as limiting the present invention,and that various modifications, changes, alterations, and equivalentembodiments can be made by those skilled in the art without departingfrom the spirit and scope of the invention. Therefore, the scope of thepresent invention should be defined by the appended claims andequivalents thereof.

What is claimed is:
 1. A thermoplastic resin composition comprising: apolyester resin; a white pigment; a core-shell structured impactmodifier, wherein the core-shell structured impact modifier has apolydimethylsiloxane rubber core; and a modified polyolefin resin,wherein the composition comprises about 1 parts by weight to about 10parts by weight of the core-shell structured impact modifier and about0.1 parts by weight to about 1 parts by weight of the modifiedpolyolefin resin, each based on about 100 parts by weight of a baseresin including the polyester resin and the white pigment, wherein theamounts of the core-shell structured impact modifier and the modifiedpolyolefin are selected to provide a weight ratio of the core-shellstructured impact modifier and the modified polyolefin resin of 6:1 toabout 20:1, and a weight ratio of the polyester resin to the whitepigment ranges from about 0.1:1 to about 10:1, wherein a molded articleformed from the thermoplastic resin composition has a difference inreflectance of about less than about 15%, as measured before/after lightirradiation (LED light source, wavelength of about 450 nm) of a platespecimen in a constant temperature/humidity oven at about 170° C. andabout 85% relative humidity (RH) for about 1,000 hours.
 2. Thethermoplastic resin composition according to claim 1, wherein thepolyester resin contains a repeat unit represented by Formula 1:

wherein Ar is a C₆ to C₁₈ arylene group, R₁ and R₃ are the same ordifferent and are each independently a C₁ to C₁₀ linear alkylene group,and R₂ is a C₃ to C₁₂ cyclic alkylene group.
 3. The thermoplastic resincomposition according to claim 1, wherein the white pigment comprisestitanium oxide, zinc oxide, zinc sulfide, white lead, zinc sulfate,barium sulfate, calcium carbonate, and/or alumina.
 4. The thermoplasticresin composition according to claim 1, wherein the modified polyolefinresin comprises a copolymer of a monomer mixture comprising an olefinand a comonomer including at least one oxygen atom forming a copolymertogether with the olefin.
 5. The thermoplastic resin compositionaccording to claim 4, wherein the comonomer comprises (meth)acrylicacid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate,hexyl (meth)acrylate, dodecyl (meth)acrylate, cyclohexyl (meth)acrylate,glycidyl (meth)acrylate, benzyl (meth)acrylate, vinyl acetate, and/orvinyl alcohol.
 6. The thermoplastic resin composition according to claim5, wherein the modified polyolefin resin includes the olefin in anamount of about 40 wt % to about 99 wt % based on a total weight of themodified polyolefin resin.
 7. The thermoplastic resin compositionaccording to claim 1, wherein the base resin further comprises inorganicfiller.
 8. The thermoplastic resin composition according to claim 7,wherein the inorganic filler is present in an amount of about 1 wt % toabout 40 wt % based on a total weight of the base resin.
 9. Thethermoplastic resin composition according to claim 7, wherein theinorganic filler comprises glass fibers, carbon fibers, glass beads,glass flakes, carbon black, clay, kaolin, talc, mica, and/orwollastonite.
 10. A molded article formed from the thermoplastic resincomposition according to claim
 1. 11. The molded article according toclaim 10, wherein the molded article is a reflector or reflector cup fora LED.
 12. The molded article according to claim 10, wherein the moldedarticle is a reflector cup for a LED.
 13. The thermoplastic resincomposition according to claim 1, wherein the weight ratio of thecore-shell structured impact modifier and the modified polyolefin resinranges from 6:1 to 15:1.
 14. The thermoplastic resin compositionaccording to claim 13, wherein a molded article formed from thethermoplastic resin composition has a difference in reflectance of 8.2%or less measured before/after light irradiation (LED light source,wavelength of about 450 nm) of a plate specimen in a constanttemperature/humidity oven at about 170° C. and about 85% relativehumidity (RH) for about 1,000 hours.
 15. The thermoplastic resincomposition according to claim 1, wherein a molded article formed fromthe thermoplastic resin composition has a difference in reflectance ofabout 1 to about 10, as measured before/after light irradiation (LEDlight source, wavelength of about 450 nm) of a plate specimen in aconstant temperature/humidity oven at about 170° C. and about 85%relative humidity (RH) for about 1,000 hours.
 16. The thermoplasticresin composition according to claim 15, wherein the core of thecore-shell structured impact modifier is a polydimethylsiloxane rubbercore, and wherein the core-shell structured impact modifier is obtainedby grafting a compound selected from the group consisting of methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylbutyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, hexyl (meth)acrylate,heptyl (meth)acrylate, octyl (meth)acrylate, and/or n-pentyl(meth)acrylate to the polydimethylsiloxane rubber core.
 17. Thethermoplastic resin composition according to claim 16, wherein: thepolyester resin includes a repeat unit represented by Formula 1:

wherein Ar is a C₆ to C₁₈ arylene group, R₁ and R₃ are the same ordifferent and are each independently a C₁ to C₁₀ linear alkylene group,and R₂ is a C₃ to C₁₂ cyclic alkylene group; the white pigment istitanium oxide; and the modified polyolefin resin is copolymer of anolefin and a comonomer selected from the group consisting of methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and/or hexyl(meth)acrylate.
 18. The thermoplastic resin composition according toclaim 17, wherein: the polyester resin is polycyclohexylenedimethyleneterephthalate (PCT) resin; the white pigment is titanium oxide; thecore-shell structured impact modifier is obtained by grafting methyl(meth)acrylate to the polydimethylsiloxane rubber core; and the modifiedpolyolefin resin is an ethylene-methacrylate copolymer.